JP5203675B2 - Position detector, position detection method, exposure apparatus, and device manufacturing method - Google Patents

Description

   The present invention relates to a position detector, a position detection method, an exposure apparatus, and a device manufacturing method.

  Projection exposure in which a pattern drawn on a reticle or photomask is projected onto a wafer or the like by a projection optical system when a semiconductor element, a liquid crystal display element, a thin film magnetic head, etc. are manufactured using photolithography technology. The device is conventionally used. At this time, exposure is performed after aligning the projection image of the mask pattern formed via the projection optical system with the alignment detection system mounted on the projection exposure apparatus with respect to the pattern already formed on the wafer. I do.

  In a projection exposure apparatus, it is required to project and expose a mask pattern onto a wafer with higher resolution as the integrated circuit becomes finer and higher in density. The minimum line width (resolution) that can be transferred by the projection exposure apparatus is proportional to the wavelength of light used for exposure and inversely proportional to the numerical aperture (NA) of the projection optical system. Therefore, the shorter the wavelength, the better the resolution. For this reason, the light sources in recent years have become KrF excimer lasers (wavelengths of about 248 nm) and ArF excimer lasers (wavelengths of about 143 nm) from the ultra high pressure mercury lamp g-line (wavelength of about 436 nm) and i-line (wavelength of about 365 nm). Yes. As a light source, F2 laser (wavelength of about 157 nm) is also being put into practical use, and in the future, extreme ultraviolet light (Extreme Ultra Violet: EUV light) with a wavelength of several nm to 100 nm is expected to be used. .

  Further, in order to further improve the resolution of the exposure apparatus, a liquid whose resolution is improved by increasing the NA by immersing a liquid having a refractive index larger than 1 in at least a part between the projection optical system and the wafer. An immersion exposure system has also appeared. In this immersion exposure apparatus, a liquid having a refractive index close to the refractive index of the photoresist layer is filled in the space between the wafer and the optical element constituting the wafer-side tip surface of the projection optical system. As a result, the effective numerical aperture of the projection optical system viewed from the wafer side increases, and the resolution can be improved.

  As described above, the resolution is further improved due to the shortening of the exposure light wavelength and the appearance of the liquid immersion method, and the wafer overlay accuracy (hereinafter referred to as overlay accuracy) is also required to be high. Usually, the overlay accuracy is required to be about 1/5 of the resolution, and as the miniaturization of semiconductor elements progresses, the improvement of the overlay accuracy becomes increasingly important.

  Two types of wafer alignment detection systems have been proposed and used. One is a so-called off-axis alignment detection system (Off-axis AA, hereinafter referred to as OA detection system) that is configured separately without using a projection optical system and optically detects alignment marks on the wafer. The second is to detect the alignment mark on the wafer using the alignment wavelength of the non-exposure light through a projection optical system called the TTL-AA (Through the Lens Auto Aligment) method as an alignment method in the i-line exposure system. Is the method.

  In the alignment system as described above, the detection signal obtained by illuminating and observing the surface to be observed, such as uneven illumination, uneven sensitivity of the light receiving element or image sensor, and distortion due to dust adhering to the detection system itself, etc. A measurement error may occur in the measurement result due to the noise component. In the current trend toward higher resolution, it is important to reduce these measurement errors. In order to reduce these measurement errors, processing for removing these noise components from the detection signal (hereinafter referred to as background correction) is performed. In the background correction, various noise components of a detection signal obtained by illuminating and observing the surface to be observed are measured in advance and stored as a background signal, and the detection signal of the alignment mark is corrected with reference to the background signal. It is processing.

The background signal for the background correction is stored for each normal alignment condition (illumination wavelength / illumination NA / detection NA), and the background correction is performed using the background signal corresponding to each alignment condition (patent) Reference 1).
JP-A-11-54418

  In a wafer alignment detection system mounted on an exposure apparatus, conditions relating to alignment performance may change due to changes in the optical system in the detection system over time, and these adjustments have been made. Conditions relating to the alignment performance include a shift component for each wavelength (hereinafter referred to as a wavelength shift difference) generated by aberration, optical axis deviation, and eccentricity of a lens, a plane parallel plate, or the like. If the background signal used before adjustment is no longer optimal, even though the alignment conditions are the same, measurement fraud may occur when alignment is performed using the previous background signal. was there.

  It is an object of the present invention to provide a position detector and a position detection method that can be detected with high accuracy even if the optical member is adjusted and conditions relating to position measurement change.

A first aspect of the present invention is a position detector that detects the position of a mark provided on a test object, an imaging unit that captures an image of the test object, and a test object on the imaging surface of the imaging unit. An optical system that forms an image of the image, a noise acquisition unit that captures a region other than the mark by using the optical system and the imaging unit in accordance with the adjustment of the optical member included in the optical system, and acquires noise information; A correction unit that corrects the image of the mark acquired using the optical system and the imaging unit using the noise information acquired by the noise acquisition unit, and the optical member can adjust the optical axis deviation of the optical system. At least one of an optical member, an optical member capable of adjusting an aberration generated in the optical system, and an optical member capable of adjusting a shift depending on a wavelength generated by the eccentricity of the optical member included in the optical system. It is characterized by that.

A second aspect of the present invention is a position detection method in which an image of a mark mounted on a test object is formed by an optical system, and the formed mark image is picked up by an image pickup unit to detect the position of the mark. Then, in response to adjustment of an optical member included in the optical system, a noise acquisition step of capturing an area other than the mark by using the optical system and the imaging unit and acquiring noise information, and using the optical system and the imaging unit look including a correction step of correcting by using the information of the acquired noise in noise acquisition process the image of the mark obtained Te, the optical member is adjustable optical element of the optical axis deviation of an optical system, the optical system At least one of an optical member capable of adjusting an aberration generated in the optical system and an optical member capable of adjusting a shift depending on a wavelength generated by the eccentricity of the optical member included in the optical system .

  ADVANTAGE OF THE INVENTION According to this invention, even if the optical member is adjusted and the conditions regarding position measurement change, the position detector and position detection method which can be detected with high precision can be provided.

[Embodiment of alignment detector used in exposure apparatus]
The position detector according to the present invention detects the position of a mark mounted on a test object in a semiconductor exposure apparatus or a liquid crystal exposure apparatus. The test object may be at least one of a reticle as an original and a wafer as a substrate. The exposure apparatus positions at least one of the original and the substrate based on the position detection result by the position detector. In the following embodiments, a wafer alignment system that detects the position of a mark mounted on a wafer of an exposure apparatus will be described.

  The alignment method when the conditions regarding the alignment performance are changed will be described with reference to the drawings.

  In the exposure apparatus of FIG. 1, reticle stage 2 supports reticle 1, and wafer stage 4 supports wafer 3. The illumination optical system 5 illuminates the reticle 1 supported on the reticle stage 2 with the exposure light, and the projection optical system 6 supports the reticle pattern image of the reticle 1 illuminated with the exposure light on the wafer stage 4. 3 is exposed to projection. The operation of the entire exposure apparatus is comprehensively controlled by the controller 17.

  In the present embodiment, a scanning type exposure apparatus (scanner) that exposes the reticle pattern formed on the reticle 1 onto the wafer 3 while moving the reticle 1 and the wafer 3 synchronously with each other in the scanning direction is used as the exposure apparatus. However, an exposure apparatus (stepper) of a type that fixes the reticle 1 and exposes the reticle pattern onto the wafer 3 can also be used.

  In the following description, the direction coinciding with the optical axis of the projection optical system 6 is the Z-axis direction, the synchronous movement direction (scanning direction) between the reticle 1 and the wafer 3 in the plane perpendicular to the Z-axis direction is the Y-axis direction, and Z A direction (non-scanning direction) perpendicular to the axial direction and the Y-axis direction is taken as an X-axis direction. The directions around the X, Y, and Z axes are the θX, θY, and θZ directions, respectively.

  A predetermined illumination area on the reticle 1 is illuminated by the illumination optical system 5 with exposure light having a uniform illuminance distribution. As the exposure light emitted from the illumination optical system 5, a KrF excimer laser, an ArF excimer laser or F2 laser having a short wavelength, or extreme ultraviolet light (Extreme Ultra Violet: EUV light) having a wavelength of several nanometers to hundred nanometers is used. sell.

  The reticle stage 2 can be two-dimensionally moved in a plane perpendicular to the optical axis of the projection optical system 6, that is, an XY plane, and can be slightly rotated in the θZ direction. The reticle stage 2 may be driven by at least one axis or may be driven by six axes. The reticle stage 2 is driven by a reticle stage drive mechanism (not shown) such as a linear motor, and the reticle stage drive mechanism is controlled by a controller 17. A mirror 7 is provided on the reticle stage 2. A laser interferometer 9 is provided at a position facing the mirror 7. The two-dimensional position and rotation angle of the reticle 1 on the reticle stage 2 are measured in real time by the laser interferometer 9, and the measurement result is output to the controller 17. The controller 17 positions the reticle 1 supported by the reticle stage 2 by driving the reticle stage driving mechanism based on the measurement result of the laser interferometer 9.

  The projection optical system 6 projects and exposes the reticle pattern of the reticle 1 onto the wafer 3 at a predetermined projection magnification β, and includes a plurality of optical elements. In the present embodiment, the projection optical system 6 is a reduction projection system having a projection magnification β of, for example, 1/4 or 1/5.

  The wafer stage 4 includes a Z stage that holds the wafer 3 through a wafer chuck, an XY stage that supports the Z stage, and a base that supports the XY stage. The wafer stage 4 is driven by a wafer stage drive mechanism (not shown) such as a linear motor. The wafer stage mechanism is controlled by the controller 17.

  A mirror 8 that moves with the wafer stage 4 is provided on the wafer stage 4. A laser interferometer 10 for XY directions and a laser interferometer 12 for Z directions are provided at positions facing the mirror 8. The position of the wafer stage 4 in the XY direction and θZ are measured in real time by the laser interferometer 10, and the measurement result is output to the controller 17. Further, the position of the wafer stage 4 in the Z direction and θX and θY are measured in real time by the laser interferometer 12, and the measurement results are output to the controller 17. The position of the wafer 3 in the XYZ directions is adjusted by driving the XYZ stage through the wafer stage drive mechanism based on the measurement results of the laser interferometers 10 and 12, and the wafer 3 supported by the wafer stage 4 is positioned. Is done.

  A reticle alignment detection system 13 is provided in the vicinity of the reticle stage 2. The reticle alignment detection system 13 passes the reticle reference mark (not shown) on the reticle 1 and the reference mark 18 for the reticle alignment detection system in FIG. 2 on the stage reference plate 11 on the wafer stage 4 through the projection optical system 6. To detect. The reticle alignment detection system 13 uses the same light source as the light source that actually exposes the wafer 3, irradiates the reticle reference mark and the reference mark 18 for the reticle alignment detection system through the projection optical system 6, and detects the reflected light. The photoelectric conversion element for mounting is mounted. The photoelectric conversion element mounted on the reticle alignment detection system 13 is, for example, a CCD camera. The reticle 1 and the wafer 3 are aligned based on the signal from the photoelectric conversion element. By aligning the position and focus of a reticle reference mark (not shown) on the reticle 1 with a reticle alignment detection system reference mark 18 on the stage reference plate 11, the relative positional relationship (X, Y) between the reticle 1 and the wafer 3 is adjusted. , Z) can be matched.

  The reference mark 18 detected by the reticle alignment detection system 13 may be a transmissive mark. If the transmission type reticle alignment detection system 14 is used, the reference mark 18 for the transmission type reticle alignment detection system can also be used.

  The transmissive reticle alignment detection system 14 is irradiated from the same light source as the light source that exposes the wafer 3, and passes through the reticle reference mark (not shown), the projection optical system 6, and the reticle alignment detection system reference mark 18. Equipped with a light intensity sensor to detect The amount of transmitted light is measured while driving the wafer stage 4 in the X direction (or Y direction) / Z direction, and the position of the reticle reference mark (not shown) on the reticle 1 and the reference mark 18 for the reticle alignment detection system and Adjust the focus.

  As described above, the relative positional relationship (X, Y, Z) between the reticle 1 and the wafer 3 can be matched by using either the reticle alignment detection system 13 or the transmission type reticle alignment detection system 14.

  The stage reference plate 11 at one corner of the wafer stage 4 is installed at substantially the same height as the surface of the wafer 3. The stage reference plate 11 includes a wafer alignment detection system reference mark 18 detected by the wafer alignment detection system 16 and a reticle alignment detection system reference mark 18 detected by the reticle alignment detection systems 13 and 14. . The stage reference plate 11 may be disposed at a plurality of corners of the wafer stage 4. One stage reference plate 11 may include a plurality of reticle alignment detection system reference marks 18 and a wafer alignment detection system reference mark 18. Here, it is assumed that the positional relationship (XY direction) between the reference mark 18 for the reticle alignment detection system and the reference mark 18 for the wafer alignment detection system is known. Further, the reference mark 18 for the wafer alignment detection system and the reference mark 18 for the reticle alignment detection system may be a common mark.

  The focus detection system 15 includes a projection system that projects detection light onto the surface of the wafer 3 and a light receiving system that receives reflected light from the wafer 3. The detection result of the focus detection system 15 is output to the controller 17. The The controller 17 drives the Z stage based on the detection result of the focus detection system 15 and can adjust the position (focus position) and tilt angle of the wafer 3 held on the Z stage in the Z-axis direction. is there.

  The wafer alignment detection system 16 includes a projection system that projects detection light onto a wafer alignment mark 19 on the wafer 3 and a reference mark 18 for the wafer alignment detection system on the stage reference plate 11 and a light receiving system for reflected light from the mark. Prepare. The detection result of the wafer alignment detection system 16 is output to the controller 17. The controller 17 can adjust the position of the wafer 3 held on the wafer stage 4 in the XY direction by driving the wafer stage 4 in the XY direction based on the detection result of the wafer alignment detection system 16. is there.

  In this embodiment, an off-axis alignment detection system (Off-axis AA, hereinafter referred to as OA detection system) is used as the wafer alignment detection system 16. However, in the present invention, the wafer alignment detection system 16 is not limited to the OA detection system.

  FIG. 3 shows in detail a wafer alignment detection system 16 as an example of a position detector according to the present invention. The light guided from the illumination light source 20 (fiber or the like) for the wafer alignment detection system passes through the first relay optical system 21, the wavelength filter plate 22, and the second relay optical system 23, and reaches the aperture stop 24. The aperture member (aperture stop) 24 hits the pupil plane (optical Fourier transform plane with respect to the object plane) of the wafer alignment detection system 16. At this time, the beam diameter at the aperture stop 24 is sufficiently smaller than the beam diameter at the illumination light source 20 (fiber or the like) for the wafer alignment detection system. FIG. 4 shows the relationship of the beam diameter at this time, and the beam diameter 39 ′ at the aperture stop 24 is sufficiently smaller than the beam diameter 39 at the light source 20.

  A plurality of types of filters having different transmission wavelength bands are inserted in the wavelength filter plate 22, and the filters are switched by a command from the controller 17. A plurality of types of apertures with different illuminations σ are prepared for the aperture stop 24, and the illumination σ can be changed by switching the apertures according to a command from the controller 17. The wavelength filter plate 22 and the aperture stop 24 are preliminarily provided with a plurality of types of filters and stops. However, this mechanism is capable of newly forming a filter and a stop.

  The light reaching the aperture stop 24 is guided to the polarization beam splitter 28 through the first illumination optical system 25 and the second illumination optical system 27. The S-polarized light perpendicular to the paper surface reflected by the polarization beam splitter 28 passes through the NA aperture 26 and the λ / 4 plate 29 and is converted into circularly polarized light, and passes through the objective lens 30 and is formed on the wafer 3. The alignment mark 19 is Koehler illuminated (illumination light is indicated by a solid line in FIG. 3). The NA aperture 26 can change the NA by changing the aperture amount. The aperture amount of the NA aperture 26 can be changed by a command from the controller 17.

  Reflected light, diffracted light, and scattered light (indicated by a one-dotted line in FIG. 3) generated from the wafer alignment mark 19 pass through the objective lens 30 again, pass through the λ / 4 plate 29, and are now P-polarized light parallel to the paper surface. And is transmitted through the polarization beam splitter 28. Through the relay lens 31, the first and second imaging optical systems 32 and 33, the coma aberration adjusting optical member 45, and the wavelength shift difference adjusting optical member 46, the transmitted light is converted from the detection signal of the wafer alignment mark 19 to a photoelectric conversion element. 34 (for example, a CCD camera).

  The photoelectric conversion element 34 constitutes an imaging unit that captures an image of the object to be examined. Various optical members from the illumination light source 20 to the wavelength shift difference adjusting optical member 46 constitute an optical system that forms an image of the object to be detected on the imaging surface of the photoelectric conversion element 34 that is an imaging unit. In the optical system, the optical member from the illumination light source 20 to the second illumination optical system 27 constitutes an illumination optical system.

  The wafer alignment detection system 16 is further provided with a signal generation unit 35, a noise acquisition unit 36, a storage unit 37, and a correction unit 38. The signal generator 35 generates a signal when an optical member included in the optical system described later is adjusted for optical axis deviation, wavelength shift difference, aberration, and the like. The noise acquisition unit 36 acquires a background signal that is noise information of the wafer alignment detection system 16 in response to the signal generated by the signal generation unit. The storage unit 37 stores background signal data acquired by the noise acquisition unit in addition to background signal data for each alignment condition. The correction unit 38 corrects the detection signal of the wafer alignment mark 19 detected by the photoelectric conversion element 34 by using the background signal under the alignment conditions at that time (so-called background correction). Therefore, when the optical member is adjusted and a signal is generated, the correction unit 38 corrects the detection signal using the background signal acquired in response to the signal. The wafer alignment detection system 16 detects the position of the wafer 3 based on the corrected detection signal and aligns the wafer 3.

  Usually, when the wafer alignment mark 19 on the wafer 3 is observed and detected by the wafer alignment detection system 16 as described above, it is interfered with monochromatic light because of the transparent layer applied or formed on the wafer alignment mark 19. Stripes are generated. Therefore, it is detected in a state where the interference fringe signal is added to the alignment signal, and cannot be detected with high accuracy. Therefore, generally, as the illumination light source 20 of such a wafer alignment detection system 16, a light source having a broad wavelength is used, and is detected as a signal with less interference fringes.

  In order to detect the wafer alignment mark 19 on the wafer 3 with high accuracy, the image of the wafer alignment mark 19 must be clearly detected. That is, the wafer alignment detection system 16 must be in focus with the wafer alignment mark 19. For this purpose, an autofocus detection system (not shown) is generally configured. Based on the detection result, the wafer alignment mark 19 is driven to the best focus surface of the wafer alignment detection system 16 to detect the wafer alignment mark 19. Is going.

  Although the description of the TTL-AA method is omitted here, it is basically different from the detection system of the OA method in that the wafer 3 is observed through the projection optical system 6.

  FIG. 5 shows an example of background correction. Reference numeral 40 in FIG. 5 shows a cross-sectional structure of the alignment mark, where the horizontal direction indicates the position and the vertical direction indicates the height. The waveform 41 in FIG. 5 indicates the signal intensity when the horizontal axis indicates the position and the vertical axis indicates the alignment mark, and the same applies to the following description. Usually, an alignment mark detection signal obtained by detecting an alignment mark such as 40 in FIG. 5 under a certain alignment condition of the wafer alignment detection system 16 is a detection signal in which an area other than the mark is seen as indicated by 41 in FIG. Become. This unevenness is caused by unevenness in the detection signal obtained by illuminating and observing the surface to be observed due to uneven illumination, uneven sensitivity in the light receiving element or image sensor, etc., and adhesion of dust, resulting in measurement errors during alignment. It was regarded as a problem.

  In the conventional background correction, an area other than the mark is imaged and a noise component (so-called background signal) of the wafer alignment detection system 16 as shown in 42 of FIG. 5 is acquired. Then, the detection signal 41 is corrected with the base signal, and the wafer is aligned by the correction detection signal as indicated by 43 in FIG. Compared with the detection signal 41 before the background correction, the correction detection signal 43 after the background correction has no unevenness in the portion other than the mark, and the measurement error at the time of alignment is reduced and high-precision alignment is possible.

  For alignment conditions (hereinafter referred to as “equipment alignment conditions”) configured in advance in the wafer alignment detection system 16, a base signal is usually prepared for each alignment condition as shown in FIG. The detection signal obtained under the alignment condition A is subjected to background correction using the background signal A optimized for the alignment condition A, and the detection signal obtained under the alignment condition B is set to the alignment condition B. Background correction is performed using the optimized background signal B. That is, the wafer alignment detection system 16 prepares an optimum ground signal for the provided alignment conditions.

  When the wafer alignment detection system 16 is mounted on an exposure apparatus, the conditions related to the alignment performance of the detection system (optical axis shift amount, wavelength shift difference, coma aberration, etc.) are adjusted to some extent. May change. Therefore, it is necessary to adjust the conditions periodically. Depending on the mark to be observed, an optimal optical axis correction may be performed for each wafer alignment mark, and the condition may be adjusted after the detection system is mounted on the exposure apparatus. That is, even if the alignment conditions such as the illumination wavelength, illumination NA, and detection NA are the same, the adjustment state related to the alignment performance such as the optical axis deviation may change. Conventionally, it has been considered that the change of the noise component is small only by the optical axis deviation correction or the like. However, in view of the recent increase in accuracy of the exposure apparatus, the change of the noise component cannot be ignored. If the adjustment state of the conditions related to alignment performance such as optical axis shift changes, the inclination of the detection signal will change, so even if the same background conditions are used, using the original background signal will not allow the optimal background correction to be fooled. Could have occurred.

  Hereinafter, an alignment method according to the present invention when an alignment performance condition is changed will be described with reference to the drawings, particularly an embodiment when an optical axis deviation amount is changed.

  First, a method for adjusting the optical axis deviation in the optical system in the wafer alignment detection system shown in FIG. 3 will be described. FIG. 7 shows an illumination optical system of the wafer alignment detection system of FIG. When there is no optical axis shift in the detection system as shown in FIG. 7, the chief ray of the illumination light of the detection system enters the wafer 3 perpendicularly. However, when the aperture member (aperture stop) 24 in the detection system is displaced as shown in FIG. 8, the chief ray of the illumination light of the detection system does not enter the wafer 3 at a certain angle θ. Incident.

  At this time, the beam diameter at the aperture stop 24 deviates from the center position of the beam diameter 39 at the illumination light source 20 (fiber or the like) for the wafer alignment detection system, as indicated by 39 ″ in FIG. Located in position. Such a state is said to have an optical axis shift in the optical system. In FIG. 8, the optical axis deviation is explained by the positional deviation of the aperture stop. However, the illumination light source 20 (fiber etc.) itself arranged at a position conjugate with the pupil in the illumination optical system is displaced as in the case of the aperture diaphragm. Even if it occurs, the optical axis shift occurs. The optical axis deviation in the optical system is adjusted by moving the position of the illumination light source 20 for the wafer alignment detection system shown in FIG. 8 or the position of the aperture stop 24 in the vertical direction that can be driven with respect to the optical axis. be able to. Thus, the adjustment of the optical axis deviation in the OA type wafer alignment detection system is performed by moving the light source 20 or the aperture stop 24 in the detection system in a direction perpendicular to the optical axis.

  Adjustment of the optical axis deviation in the optical system in the wafer alignment detection system is performed using position information (hereinafter referred to as defocus characteristics) of each alignment mark with respect to each defocus position. The defocus characteristic that is an index of the optical axis deviation of the optical system will be described with reference to FIGS. In order to inspect the defocus characteristic, measurement may be performed while defocusing the alignment mark of the chrome pattern. The alignment mark of the chrome pattern is configured on the stage reference plate 11 in the apparatus, and defocus characteristic data can be easily obtained on the exposure apparatus. Furthermore, the defocus characteristic can be similarly obtained and corrected for the alignment mark on the actual exposure wafer to be actually exposed. It has been found that the difference in defocus characteristics between the chrome pattern formed on the stage reference plate 11 and the actual exposure wafer is caused by the aberration component remaining in the detection system, the difference in the cross-sectional structure of the alignment mark, and the like. . FIG. 9 shows a detection signal at the alignment mark of the chrome pattern. The detection signal 50 in FIG. 9 is a symmetric detection signal detected by an ideal optical system in which no optical axis deviation remains in the optical system in the wafer alignment detection system. A detection signal obtained by defocusing the detection signal 50 in the plus direction is a detection signal 51, and a detection signal obtained by defocusing in the minus direction is a detection signal 52. Although the defocused detection signals 51 and 52 have a lower contrast of the detection signal than the detection signal 50, the symmetry of the detection signal is not lost because the optical axis shift does not remain in the optical system. That is, the measurement center positions of the detection signals 51 and 52 are the same as the detection signal 50. FIG. 10 shows the measurement center position for the defocus at this time, and the measurement center position of the detection signal takes a constant value regardless of the defocus, as shown by 53. The inclination of the detection signal with respect to the measurement center position 53 with respect to the defocus is the defocus characteristic. In this case, the defocus characteristic is zero. If there is no change in the measurement center position with respect to defocus as shown in FIG. 10, even if defocus occurs during wafer alignment, no positional deviation occurs.

  The detection signal 54 in FIG. 11 shows a case where the optical axis deviation remains in the optical system in the wafer alignment detection system. A detection signal obtained by defocusing the detection signal 54 in the plus direction is a detection signal 55, and a detection signal obtained by defocusing in the minus direction is a detection signal 56. The defocused detection signals 55 and 56 not only lower the contrast, but also become asymmetric detection signals due to the influence of the optical axis shift in the detection system. The measurement center positions of the detection signals 55 and 56 at this time cannot take the same position as the detection signal 54. FIG. 12 shows the measurement center position for defocus at this time, and the measurement signal center position of the detection signal takes a value depending on defocus, such as 57. The inclination with respect to the 57 defocus is a defocus characteristic, and in this case, has a certain defocus characteristic value. When there is a change in the measurement center position with respect to defocus as shown in FIG. 12, no position shift occurs in the best focus. However, since a slight defocus occurs during actual wafer alignment, a positional shift occurs in such a case. Since this defocus characteristic can be used as an index representing the optical axis deviation of the detection system, the optical axis deviation can be adjusted so that the defocus characteristic becomes zero. .

  A specific example of the background correction is shown below in FIG. Normally, an alignment mark detection signal obtained by detecting an alignment mark such as 40 in FIG. 13 under a certain alignment condition of the wafer alignment detection system 16 is a detection signal in which unevenness is seen in a non-mark area as indicated by 60 in FIG. . This unevenness is due to unevenness in the detection signal obtained by illuminating and observing the surface to be observed due to unevenness in illumination, unevenness in the sensitivity of the light receiving element or image sensor, etc., or adhesion of dust. It becomes.

  In the conventional background correction, an area other than the mark is observed under the alignment condition, and a noise component (so-called background signal) of the wafer alignment detection system 16 such as 61 in FIG. 13 is stored in advance. Then, the detection signal 60 is corrected, and the wafer is aligned as a correction detection signal like 62 in FIG. Compared with the detection signal 60 before the background correction, the correction detection signal 62 after the background correction has no unevenness in the non-marked portion, and the measurement fraud in the alignment is reduced, thereby enabling highly accurate alignment.

  For alignment conditions preconfigured in the wafer alignment detection system 16, a base signal is usually prepared for each alignment condition as shown in FIG. For the detection signal obtained under the alignment condition C, the background correction is performed using the background signal C optimized for the alignment condition C.

  However, the optical axis deviation of the wafer alignment detection system may be adjusted on the exposure apparatus. In this case, even if the alignment conditions such as the illumination wavelength, the illumination NA, and the detection NA are the same, the base before adjustment of the optical axis deviation is performed. High-precision alignment may not be possible using signals.

  The detection signal 63 in FIG. 15 is measured under the same alignment condition C as the detection signal 60 in FIG. 13, but is acquired in a state where the adjustment of the optical axis deviation of the wafer alignment detection system is different. The detection signal 63 in FIG. 15 differs from the detection signal 60 in FIG. 13 in the adjustment state of the optical axis deviation of the detection system, and therefore the detection signal is different even under the same alignment conditions. When the background correction is performed using the background signal 61 before adjusting the optical axis deviation of the detection system in a state like the detection signal 63 in FIG. 15, an inclination is applied to an area other than the mark as in the detection signal 64. This results in an asymmetric detection signal. Such an asymmetric detection signal causes a measurement error during alignment. As described above, if the adjustment state of the optical axis deviation of the detection system is changed even under the same alignment condition, it is necessary to re-acquire the ground signal in the adjusted state of the optical axis deviation after the change.

  In the present embodiment, the base signal CC is reacquired in response to a change in the adjustment state of the optical axis deviation under the alignment condition C (FIG. 16). The re-extracted background signal CC is optimized to the one in which the adjustment state of the optical axis deviation of the alignment condition C is changed, and appropriate background correction can be performed. The detection signal 63 in FIG. 17 differs from the detection signal 63 in FIG. 13 in the adjustment state of the optical axis deviation of the detection system as in the detection signal 60 in FIG. The detection signal 63 is subjected to background correction using the background signal 65 that has been re-corrected in the state of the optical axis shift after the change using the background signal 65. Then, a symmetric correction detection signal 66 without unevenness or inclination in the non-mark area is obtained. Compared with the correction detection signal 64 in which the background correction is performed with the background signal 61 acquired before the optical axis deviation adjustment of the detection system, the background correction is performed with the background signal 65 acquired in accordance with the optical axis deviation adjustment of the detection system. The performed correction detection signal 66 has no unevenness or inclination in an area other than the mark. Therefore, highly accurate alignment is possible.

  In other words, even when the optical axis misalignment state of the wafer alignment detection system is changed under the same alignment conditions, correction detection without unevenness or inclination of the detection signal is obtained by acquiring the optimal base signal in the optical axis misalignment state after the change. A signal can be obtained.

  In the above description, the description has been given of the case where the background signal is read again in response to the change of the optical axis deviation state of the wafer alignment detection system under the same alignment condition. However, the present invention only changes the optical axis deviation state. However, the present invention is not limited to re-acquiring the ground signal according to the above. In addition to the adjustment of the optical axis deviation, the base signal is re-acquired when the coma aberration amount is changed by the optical member 45 capable of adjusting the coma aberration in the detection system. The coma aberration adjustment of the detection system is performed by moving the optical member 45 capable of adjusting the coma aberration perpendicularly to the optical axis direction. In addition, the base signal is re-acquired even when the wavelength shift difference is changed by the optical member 46 for adjusting the shift depending on the wavelength generated by the eccentricity of the optical member included in the optical system. The wavelength shift difference adjusting optical member 46 has a plurality of wedge optical members, and adjacent wedge surfaces of different wedge optical members are inclined at a predetermined angle from a direction perpendicular to the detection optical axis, and the adjacent wedge surfaces are They are arranged in parallel. The optical member 46 for adjusting the wavelength shift difference can adjust the wavelength shift difference by adjusting the interval between the wedge members.

  According to the present embodiment, it is possible to perform optimum background correction regardless of the state of the detection system, and it is possible to always perform highly accurate alignment with less measurement fraud.

  In addition, when the conditions related to alignment performance such as the optical axis misalignment amount, coma aberration amount, and wavelength shift difference of the wafer alignment detection system are changed, the sequence for acquiring the background signal is automatically performed when the conditions are changed. The sequence may be acquired.

[Device Manufacturing Embodiment]
Next, with reference to FIGS. 18 and 19, an embodiment of a device manufacturing method using the above-described exposure apparatus will be described. FIG. 18 is a flowchart for explaining how to fabricate devices (ie, semiconductor chips such as IC and LSI, LCDs, CCDs, and the like). Here, a semiconductor chip manufacturing method will be described as an example.

  In step 1 (circuit design), a semiconductor device circuit is designed. In step 2 (mask production), a mask is produced based on the designed circuit pattern. In step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon. Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer using the mask and the wafer by the above exposure apparatus using the lithography technique. Step 5 (assembly) is referred to as a post-process, and is a process for forming a semiconductor chip using the wafer produced in step 4, and an assembly process such as an assembly process (dicing, bonding), a packaging process (chip encapsulation), or the like. including. In step 6 (inspection), the semiconductor device manufactured in step 5 undergoes inspections such as an operation confirmation test and a durability test. Through these steps, a semiconductor device is completed and shipped (step 7).

  FIG. 19 is a detailed flowchart of the wafer process in Step 4. In step 11 (oxidation), the surface of the wafer is oxidized. In step 12 (CVD), an insulating film is formed on the surface of the wafer. In step 13 (electrode formation), an electrode is formed on the wafer by vapor deposition. In step 14 (ion implantation), ions are implanted into the wafer. In step 15 (resist process), a photosensitive agent is applied to the wafer. Step 16 (exposure) uses the exposure apparatus to expose a circuit pattern on the mask onto the wafer. In step 17 (development), the exposed wafer is developed. In step 18 (etching), portions other than the developed resist image are removed. In step 19 (resist stripping), the resist that has become unnecessary after the etching is removed. By repeatedly performing these steps, multiple circuit patterns are formed on the wafer.

It is a figure which shows schematically the structure of exposure apparatus. It is a figure which shows a wafer and a stage reference | standard plate. It is a figure which shows the structure of a wafer alignment detection system in detail. It is the figure which showed the size of the beam in a light source and a pupil position. It is the figure which showed the example of a wafer alignment mark, a detection signal, a background signal, and a correction | amendment detection signal. It is the figure which showed the example of the background signal corresponding to alignment conditions. It is the figure which showed the illumination part of the wafer alignment detection system when there is no optical axis shift. It is the figure which showed the illumination part of the wafer alignment detection system in case there exists optical axis offset. It is the figure which defocused the detection signal detected with the optical system without an optical axis shift. It is the figure which showed the center position of the detection signal with respect to the defocus in the detection signal of FIG. It is the figure which defocused the detection signal detected with the optical system with an optical axis offset. It is the figure which showed the center position of the detection signal with respect to the defocus in the detection signal of FIG. It is the figure which showed the example of a wafer alignment mark, a detection signal, a background signal, and a correction | amendment detection signal. It is the figure which showed the example of the background signal corresponding to alignment conditions. It is the figure which showed the example of a wafer alignment mark, a detection signal, a background signal, and a correction | amendment detection signal. It is the figure which showed the example of the background signal corresponding to alignment conditions. It is the figure which showed the example of a wafer alignment mark, a detection signal, a background signal, and a correction | amendment detection signal. It is a flowchart for demonstrating manufacture of the device using an exposure apparatus. 19 is a detailed flowchart of the wafer process in Step 4 in the flowchart shown in FIG. 18.

Explanation of symbols

1: Reticle (original)
2: Reticle stage 3: Wafer (substrate)
4: Wafer stage 5: Illumination optical system 6 of exposure apparatus: Projection optical system 7, 8: Mirror 9, 10, 12: Laser interferometer 11: Stage reference plate 13: Reticle alignment detection system 14: Transmission type reticle alignment detection System 15: Focus detection system 16: Wafer alignment detection system (position detector)
17: controller 18: reticle, reference mark 19 for wafer alignment detection system 19: wafer alignment mark 20: illumination light source 21 for wafer alignment detection system 21: first relay optical system 22: wavelength filter plate 23: second relay optical system 24: Aperture stop (aperture member)
25: first illumination optical system 26: NA aperture 27: second illumination optical system 28: polarization beam splitter 29: λ / 4 plate 30: objective lens 31: relay lens 32: first imaging optical system 33: second connection Image optical system 34: photoelectric conversion element (imaging unit)
35: Signal generation unit 36: Noise acquisition unit 37: Storage unit 38: Correction units 39, 39 ′, 39 ″: Beam diameter 40: Alignment marks 41, 60, 63: Detection signals 42, 61, 65: Background signal 43 62, 64, 66: Correction detection signal 45: Optical member 46 for adjusting coma aberration: Optical member 50 for adjusting wavelength shift difference: Symmetrical detection signal 51: Detection signal 52 where detection signal 50 is defocused 52: Detection signal 50 is defocused in the direction opposite to the detection signal 51. 53: A line 54 indicates a change of the center position with respect to the defocus. 54: Asymmetric detection signal 55. Detection signal 56 is defocused. 56: Detection signal. 54 is a defocused detection signal 57 in the direction opposite to the detection signal 55: a line showing a change in the center position with respect to the defocus

Claims (8)

A position detector for detecting the position of a mark provided on a test object,
An imaging unit that captures an image of the test object;
An optical system for forming an image of the test object on an imaging surface of the imaging unit;
A noise acquisition unit that captures an image of a region other than the mark by using the optical system and the imaging unit in response to adjustment of an optical member included in the optical system;
A correction unit that corrects the image of the mark acquired using the optical system and the imaging unit using information on noise acquired by the noise acquisition unit;
Equipped with a,
The optical member includes an optical member capable of adjusting an optical axis shift of the optical system, an optical member capable of adjusting an aberration generated in the optical system, and a wavelength generated by the eccentricity of the optical member included in the optical system. A position detector comprising at least one of optical members capable of adjusting a shift depending on the position. The optical member capable of adjusting the optical axis deviation of the optical system is at least one of a light source and an aperture member that are arranged at a position conjugate with the pupil in the illumination optical system and can be driven in a direction perpendicular to the optical axis. The position detector according to claim 1. The optical member capable of adjusting the shift depending on the wavelength generated by the eccentricity of the optical member included in the optical system is a plurality of wedge optical members, and the shift is adjusted by adjusting an interval between the wedge optical members. The position detector according to claim 1 or 2, characterized by the above. A signal generator that generates a signal in response to adjustment of an optical member included in the optical system;
The noise acquisition unit, any of claims 1 to 3, characterized in that imaging a region other than the mark to acquire information of the noise by using the optical system and the image pickup unit in response to said signal or position detector according to (1). A storage unit for storing noise information acquired by the noise acquisition unit;
Wherein the correction unit includes a position detector according to any one of claims 1 to 4, characterized in that to correct the image of the mark by using the information of the noise that has been stored by the storage unit. A position detection method in which an image of a mark mounted on a test object is formed by an optical system, an image of the formed mark is captured by an imaging unit, and the position of the mark is detected.
A noise acquisition step of imaging a region other than the mark using the optical system and the imaging unit in accordance with the adjustment of an optical member included in the optical system and acquiring noise information;
A correction step of correcting the image of the mark acquired using the optical system and the imaging unit using the noise information acquired in the noise acquisition step;
Only including,
The optical member includes an optical member capable of adjusting an optical axis shift of the optical system, an optical member capable of adjusting an aberration generated in the optical system, and a wavelength generated by the eccentricity of the optical member included in the optical system. A position detection method characterized in that the position detection method is at least one of optical members capable of adjusting the shift depending on the position. An exposure apparatus that projects and exposes a pattern formed on an original plate onto a substrate,
The position detector according to any one of claims 1 to 5 , wherein at least one of the original plate and the substrate is used as the test object, and the position of the mark is detected.
An exposure apparatus that positions at least one of the original and the substrate based on a position detection result by the position detector. A step of exposing the substrate using the exposure apparatus according to claim 7 ;
Developing the exposed substrate;
Device manufacturing method comprising a.

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